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Bis-cyclometalated iridium(III) complexes with terpyridine analogues: syntheses, structures, spectroscopy and computational studies

Bis-cyclometalated iridium(III) complexes with terpyridine analogues: syntheses, structures, spectroscopy and computational studies
Bis-cyclometalated iridium(III) complexes with terpyridine analogues: syntheses, structures, spectroscopy and computational studies
Two ligands based upon a 2,6-disubstituted pyridine bridge introduce bis-quinoxalinyl units in a fashion that yields analogues to the archetypal terdentate ligand, 2,2′:6′,2′′-terpyridine. The ligands were synthesised from the key intermediate 2,6-bis(bromoacetyl)pyridine: a new, high-yielding route is described for this reagent. Two ligand variants (differentiated by H/Me substituents on the quinoxaline ring) were explored as coordinating moieties for iridium(III) in the development of luminescent complexes. Computational studies (DFT approaches employing B3LYP, B3LYP/LANL2DZ, and M062X/LANL2DZ levels) were used to investigate the geometric and coordination mode preferences of the new ligands and two possibilities arose from theoretical investigations: [Ir(N^N^N)2]3+ and [Ir(N^N^C)2]+, with the former predicted to be more energetically favourable. Upon synthesis and isolation of the Ir(III) complexes, X-ray crystallographic studies revealed coordination spheres that were cyclometalated, the structures both showing a [Ir(N^N^C)2]PF6 arrangement. Further spectroscopic characterization via NMR confirmed the ligand arrangements in the complexes, and photophysical studies, supported by DFT, showed that a mixture of metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT) character is likely to contribute to the emission features of the complexes, which phosphoresce orange-red (λem = 580–618 nm). The emission wavelength was influenced by the substituents on the quinoxaline ring (H vs. Me), thereby implying further tuneability is possible with future ligand iterations.
2046-2069
39718-39727
Otaif, Haleema Y.
1b365536-1683-40d5-b6d2-3f869cdac579
Adams, Samuel J.
cc59becc-f0f5-4900-85c5-da342fdf39aa
Horton, Peter
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Beames, Joseph M.
73b04545-4859-44ad-999e-551f82924c29
Pope, Simon J.A.
db9a489c-29ba-41cd-a96a-623bace0889d
Otaif, Haleema Y.
1b365536-1683-40d5-b6d2-3f869cdac579
Adams, Samuel J.
cc59becc-f0f5-4900-85c5-da342fdf39aa
Horton, Peter
154c8930-bfc3-495b-ad4a-8a278d5da3a5
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Beames, Joseph M.
73b04545-4859-44ad-999e-551f82924c29
Pope, Simon J.A.
db9a489c-29ba-41cd-a96a-623bace0889d

Otaif, Haleema Y., Adams, Samuel J., Horton, Peter, Coles, Simon J., Beames, Joseph M. and Pope, Simon J.A. (2021) Bis-cyclometalated iridium(III) complexes with terpyridine analogues: syntheses, structures, spectroscopy and computational studies. RSC Advances, 11 (63), 39718-39727. (doi:10.1039/D1RA07213G).

Record type: Article

Abstract

Two ligands based upon a 2,6-disubstituted pyridine bridge introduce bis-quinoxalinyl units in a fashion that yields analogues to the archetypal terdentate ligand, 2,2′:6′,2′′-terpyridine. The ligands were synthesised from the key intermediate 2,6-bis(bromoacetyl)pyridine: a new, high-yielding route is described for this reagent. Two ligand variants (differentiated by H/Me substituents on the quinoxaline ring) were explored as coordinating moieties for iridium(III) in the development of luminescent complexes. Computational studies (DFT approaches employing B3LYP, B3LYP/LANL2DZ, and M062X/LANL2DZ levels) were used to investigate the geometric and coordination mode preferences of the new ligands and two possibilities arose from theoretical investigations: [Ir(N^N^N)2]3+ and [Ir(N^N^C)2]+, with the former predicted to be more energetically favourable. Upon synthesis and isolation of the Ir(III) complexes, X-ray crystallographic studies revealed coordination spheres that were cyclometalated, the structures both showing a [Ir(N^N^C)2]PF6 arrangement. Further spectroscopic characterization via NMR confirmed the ligand arrangements in the complexes, and photophysical studies, supported by DFT, showed that a mixture of metal-to-ligand charge transfer (MLCT) and intra-ligand charge transfer (ILCT) character is likely to contribute to the emission features of the complexes, which phosphoresce orange-red (λem = 580–618 nm). The emission wavelength was influenced by the substituents on the quinoxaline ring (H vs. Me), thereby implying further tuneability is possible with future ligand iterations.

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Accepted/In Press date: 2 December 2021
e-pub ahead of print date: 13 December 2021
Published date: 13 December 2021
Additional Information: Funding Information: The Leverhulme Trust are thanked for funding (RPG-2015-359). The EPSRC National Mass Spectrometry Service at Swansea University is also thanked. Dr Thomas Stonelake is thanked for some initial contributions to the computational work. Publisher Copyright: © The Royal Society of Chemistry 2021.

Identifiers

Local EPrints ID: 452863
URI: http://eprints.soton.ac.uk/id/eprint/452863
ISSN: 2046-2069
PURE UUID: 333fe231-9446-4129-95e8-720a5e8421db
ORCID for Peter Horton: ORCID iD orcid.org/0000-0001-8886-2016
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272

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Date deposited: 06 Jan 2022 17:31
Last modified: 06 Jun 2024 01:38

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Contributors

Author: Haleema Y. Otaif
Author: Samuel J. Adams
Author: Peter Horton ORCID iD
Author: Simon J. Coles ORCID iD
Author: Joseph M. Beames
Author: Simon J.A. Pope

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